1. Field of the Invention
The present invention relates to cathodic protection, and particularly to an anode assembly for the cathodic protection of offshore steel piles and the like which provides stability and protection for the anode in a submerged, underwater environment.
2. Description of the Related Art
Cathodic protection (CP) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded “sacrificial metal” to act as the anode. Cathodic protection systems protect a wide range of metallic structures in various environments. Common applications include steel water or fuel pipelines, steel pier piles, offshore steel piles, ship and boat hulls, offshore oil platforms and onshore oil well casings, offshore wind farm foundations and metal reinforcement bars in concrete buildings and structures.
FIG. 2 illustrates a typical cathodic protection arrangement used for protecting submerged steel structures, such as offshore steel piles and the like. In FIG. 2, the steel structure 120 to be protected is partially submerged in seawater W. An external support 122 is positioned above the water (i.e., in a dry, above-water environment) and sacrificial anode 112 is suspended therefrom by insulated anode cable 114. A direct current (DC) power source 116 is electrically connected on its positive side to the anode via insulated anode cable 114, and the negative side of DC power source 116 is in electrical contact with the steel structure 120 via negative return cable 118. The iron in the steel is the primary cause of corrosion in the partially submerged portion of the steel structure 120. The corrosion of the iron begins with a breakdown of the iron into iron ions and free electrons: 2Fe→2Fe+++4e−. The free electrons travel through the established conductive path to less active sites, where oxygen gas is converted to oxygen ions (through combination with the four free electrons), which combines with water to form hydroxyl ions: O2+4e−+2H2O→4OH−. Recombination of these ions at the active surface yield the iron-corrosion product ferrous hydroxide through iron combining with oxygen and water to form the ferrous hydroxide: 2Fe+O2+2H2O→2Fe(OH)2.
Aluminum is a common material used in the manufacture of sacrificial anodes, such as anode 112. Using aluminum as an example, cathodic protection begins with a reaction at the aluminum surface, resulting in four aluminum ions plus twelve free electrons: 4Al→4Al++++12e−. At the steel surface, oxygen gas is converted to oxygen ions which combine with water to form hydroxyl ions: 3O2+12e−+6H2O→12OH−. As long as the current (i.e., the free electrons) arrives at the cathode (i.e., the steel structure 120) faster than oxygen is arriving, no corrosion will occur.
In the particular CP application illustrated in FIG. 2, cathodic protection of offshore steel piles presents a unique challenge for implementing CP. Specifically, the particular submerged, underwater environment makes it difficult to maintain proper positioning of the anode. The anodes used with such offshore steel piles often become entangled in fishing nets, for example, as well as being susceptible to support cable failure due to strong currents created by passing boats, in addition to snagging by underwater materials. Thus, an anode assembly for cathodic protection of offshore steel piles solving the aforementioned problems is desired.